Protists are ... Characteristics and features of the structure

At first glance it seems that modern taxonomy has already determined all the main taxa and has no disputable issues. But this is not so. Have you heard of such a systematic unit as protists? If not, then our article is for you.

History of the discovery

Protists are a concept that was first introduced into science by German naturalist Ernst Haeckel. It happened in 1886. At that time, two kingdoms of living nature were already known : Plants and Animals. All other living organisms scientist and attributed to protists. However, science did not stand still. Systematics distinguished new leading signs, created taxa. And in 1969, the American ecologist Robert Whittaker described the protists already in the modern view. By the way, this scientist is called the author of the "five kingdoms" system. This classification of all living things is still relevant today.

Characteristics protista

Protists include all organisms whose body does not form real tissues. And it does not matter how many cells they are formed. The structure of protists is characterized by the presence of a nucleus. Among the plants, algae belong to this group. Heterotrophic protists are represented by the simplest animals and mushroom-like organisms.

The structure of algae

The description of the protists will begin with the very first plants that appeared on the planet, algae. Among them there are multicellular representatives. This is chlamydomonas and chlorella. Despite the fact that the whole of their body is represented by a single cell, they carry out all processes of life. This breath through the shell, motion with the flagellum, autotrophic nutrition, reproduction by dividing in half or sporulation. Multicellular algae are more diverse. In their body, the cells are connected anatomically, but they do not form tissues. Such structures are called thallus, or thallus.

Heterotrophic protists

This group includes species that are able to eat only ready-made organic substances. Heterotrophic protists are single-celled, or protozoan animals. Despite the name, their structure is also quite difficult. One of the most common representatives of protozoa is the infusoria shoe. Like all animals, their surface apparatus is represented by a plasma membrane and a pellicle representing a compacted layer of the cytoplasm. Constant organelles of these protists are digestive and contractile vacuoles. The former perform enzymatic cleavage of organic substances, and the second - the regulation of osmotic pressure and water-salt metabolism.

Infusorians even have a sexual process, which takes place in the form of conjugation. Two animals approach each other, a cytoplasmic bridge is formed between them, according to which the nuclei exchange genetic information. The organelles of the heterotrophic protista movement are very diverse. Infusorians have numerous cilia, euglens have the only flagella. But the amoeba proteus forms unstable protrusions of the cytoplasm, which are called pseudopods, or pseudopodia.

Mushroom-like protists

This group of protists resembles real fungi remotely. For example, the body of labyrinths is represented by mesh wandering plasmodia. And the cell wall of oomycetes consists of hard cellulose. In addition, during asexual reproduction they form mobile zoospores. These signs are also characteristic for half-order of hyphohytridia, most of which are intracellular parasites of algae and invertebrate animals.

Unique properties

Protists are organisms that have very unusual symptoms. These include pseudopodia of mushroom-like labyrinths. They merge with similar structures of neighboring cells, forming an entire network. Representatives of the order of chrysophytes are supplied with a special outgrowth, which is called the haptoneme. It consists of microtubules surrounded by a channel of the endoplasmic reticulum. Dinophyte algae exhibit the inherent structure of the nucleus, the chromosomes in which are always in a spiraling state.

What is polyphilia?

Very often the protista is called the polyphyletic group, or taxon. This means that its composition includes organisms that have proven to be related to representatives of other systematic units that are not included in this one. Thus, protozoa belong to the animal kingdom, and algae belong to the plant kingdom. Polyphyletic taxa are not part of modern taxonomy, since their representatives do not have a common ancestor. Examples of such groups are cold-blooded animals or autotrophic bacteria.

So protists are eukaryotic organisms that do not form real tissues. Among them there are single and multicellular species, auto- and heterotrophs. To modern representatives protists include algae, protozoa animals and mushroom-like organisms.